Electrolytic process of producing alkali and alkaline earth metals



Oct. 28, 1952 MlNNlcK ETAL 2,615,838

ELECTROLYTIC PROCESS OF PRODUCING ALKALI AND ALKALINE EARTH METALS FiledMay 2'7, 1946 MAKE U P SOLVENT l ALKALI METAL OR ALKALINE EARTHANHYDROUS METAL THIOCYANATE LIQUID SOLVENT OR PERCHLORATE O+-ELECTRICALH E NERGY CELL CATHODE PRODUCT ANOLYTE con-mums SOLVENT SGN' OR CLO;IONS IN soLvENT ---"T SOLVENT I l l SOLVENT REMOVAL EVAPORATJR:

ALKALI METAL OR ALKALINE EARTH METAL Ho OXIDE HYDROXIDE on I; CARBONATEI V ANHYDRCUS 'SOLVENT REACTOR ALKALI METAL OR ALKALINE EARTH METALTHIOCYANATE on PER- T V cHL RA E DRYER ALKALI METAL OR ALKAL'NE EARTHMETAL PRODUCT INVENTORS LEONARD JOHN MINNICK CYRIL PRESGRAVE'. BY THEIRATTORNEYS Patented Oct. 28, 1952 ELECTROLYTIC PROCESS OF PRODUCING.ALKALLAND ALKALINE EARTHYMETALS Leonard John Minnick, Cheltenham andCyril Presgrave, East Whitemarsh Township, Mont gomery County, Pa.,assignors to G. and W. H.

Corson, Inc., Plymouth Meeting,-..I{a.,=.a corpora rationofiDelaware.

Applioation'May 27,, 1946, Serial No; 6725704 8 Claims. :J-Cl.20.4.i'59): -.-i

The present invention relates to' a process for the'production of alkaliand alkaline earth met als,'-and more particularly itrelates to aprocess The processes at present available for the preparationof alkaliand alkaline earth metals aregenerally divisible into two typesfirst,the

methodsinvolving chemical reactions and, sec- 0nd, those employing theuse of an electric current:-- The former type of method involvesreduction' reactions conducted in retorts under specialatmospheres orhigh vacuum, and'many problems are involved in the commercial op-'eration' of this type oi-process. The latter type of method'involves,-so far as commercial practice is-concerned; chiefly theelectrolysis, in the molten state, of an anhydrous salt of the metal.

Other methods for producing alkali and alkaline earth metals byelectrolysis in both aqueous and non-aqueous solvents have beensuggested.- Usually, the use of an aqueous solution-is impractical sincethere is a strong tendency for hydrogen to be evolved at the cathode,and the releaseof hydrogen is accompanied by decomposition of thesolvent and the conversion of the-metal into the hydroxide. Severalideas have also been described in which a co-deposit of hydrogen and thealkali metal is formed at thecathodeduring the electrolysis of an alkalimetal salt dissolved-in a non-aqueous solvent-= such as propyl or otherhigher alcohol; In such cases; high voltage, with consequent high powerconsumption,- is required and the co-plating of the hydrogen with themetal is also undesirable.

One object ofthe present invention is to provide an economical processfor the production of alkali and alkaline earth metals by theelectrolysis ofa non-aqueous liquid comprising anhydrous' liquidammonia;methylami-ne,- prop-yl-- amine, or pyridine combine'd-with a salt. ofthe A further object of: the invention istoprovide J anelectrolytichprocess for the preparation of alkali and :alkaline' earthmetals which may be conducted lat relatively high current densities.

andwwith relativ.elyr;-low power consumption to produce cacathode-product;substantially. free from :contami-nation by:unelectro'lyzed salt:

AnOt11Br. .QbjeCt-;0r the invention: is. to: provide r i a method. forproducingaalkalizuand alkaline earth metals as the=cathode productgwincon-t 2 junction'fwith the product'oniofs: an: anode profile-""- uctthat mayflireadilyzbe-employed;to":prepare an. alkali; or. alkaline;earth metal salt available'afor recyclingiinwthe process. Anothersobjectofzthetinvention is to. provide P a method for the-productionlof;alkalin andalka line. earth 'metalsifrom-z salts; :of the metal-;that: can be prepared: without: difiiculty from; inexapensiveizrawmaterials:

A still::furtherzobjectmof :the: invention; is to makezeavailable 1a.process for the'fielectrolytic; production-50f alkalitaand alkaline--earth:metalsfrom :salts thereofteven': when :the salts are not; :L:anhydrous. Still anotherv object of. the inventioniis lto. pros 1;. videa- -.process-'.:by whicht'.;.a..substantially?pure. solution: orpaste;-: :xcomprisin'g the 1" :alka'lizl alkalineearthm'etaharldthe-solvent of: the'ele trolyte; maybe prepared; twhichnsolutioniior:pa'ste: may: be used :in the industriesrhrimay bereadily convertedintoian alkaliior alkaline'earthmetal of a high state of purity, merelyby. evaporation of the solvent.

Other: objectstincludihg: the provision of a1; cyclic chemicalrandelectrochemical: process for 1 the preparation :of :alkali and alkalineearth-met-: als,. wi1l be apparent-from a consideration"- of thisspecification and the claims;

The Ilprocess of the present invention "is ap- I plicable for use in theproduction :of: any 1 of the I various alkali .zor. alkalinei earth.metals; namely-,4, lithium; sodiumppotassium; caesium; rubidium,- i.calcium, strontium, 'and.'barium;::and ofxalloys orrw mixturesthereof;iii.

In accordancmiwith the. invention, a cathode productxcomprisingzanfialkaliaror alkaline earth '1 metal substantially 7 uncontaminated byunelec-z trolyzed salt is: prepared by the electrolysis: ":01? anelectrolyterto form a: cathode. and an anode: products The electrolyteis a non-aqueous 1iq-- uid comprising :an anhydrous liquidselected-from: i the group. consisting of. ammonia;methylaminaiethylamine'; and .pyridine 'combined'rwith a salt I of the"metal: selected ifrom'the' group. :consisting of the.perch'loraterand;thiocyanate, and'in such :3 an electrolyte :theconcentration of salt-therein v provides a solution .in-zwhich thecathode: prod- T uct is substantially insoluble; rThe cathode 1 product;as will .be. further a discussed; 'may abe a r. bronze liquid, a :paste,or the metal itself v.Since the liquid. orpasteiis'substantiallyinsolubleiin; and hasai-lower specific :gravity thanthetelece trolyte; it; floats; thereoni-irand;therefore; theip. product;substantially free ..from-.unelectrolyzed A salt,';1may be, easilyseparated from the .electro: n:

3 lyte. The anode product comprising the anhydrous liquid, the anion ofthe metal salt and its associated solvated proton is separated from thecell, and the anion and its associated solvated proton are reacted withthe oxide, hydroxide Or carbonate of the desired metal to form thecorresponding metal salt. This salt, in substantially anhydrous form, isthen used as source material in the process.

The process of the present invention will be more clearly understoodfrom a consideration of the drawing which illustrates the process bymeans of a flow sheet diagram.

Referring to the drawing, there is shown an electrolytic cell, thecathode and anode of which are connected to a source of electricalenergy. The cell is equipped with cooling means. The anhydrous liquidsolvent of the type described herein is fed to the cell, and the alkalimetal or alkaline earth metal thiocyanate or perchlorate obtained asdescribed herein is also fed to the cell. During electrolysisthere isformed a cathode product comprising the desired metal, and anodeproduct. Nitrogen may also be formed when ammonia is present. Thecathode product is removed from the cell and the metal separated fromadhering solvent. The solvent may be recycled to the cell as shown. Theanode product comprises solvent and the thiocyanate or perchlorateanion, and the anion is converted to the alkali metal or alkaline earthmetal salt by reaction between the anion and the oxide, hydroxide orcarbonate of the desired alkali metal or alkaline earth metal. Thisreaction may take place in the cell itself as more fully discussedhereinafter, or may take place outside the cell as shown in the drawingand as also more fully discussed hereinafter. If this reaction takesplace outside the cell, the reaction medium may comprise the entireanode product to which water may be added, or excess solvent may firstbe removed, as in an evaporator, and recycled, following Which theremaining anode product is mixed with water which serves as the reactionmedium. Any of the anhydrous solvent remaining after the reaction may berecycled for re-use in the process. In any event, the anion is convertedto the alkali metal or alkaline earth metal salt which is dried andreused in the process. In view or the fact that some of the solvent maybe destroyed during the electrolysis, make-up solvent may be added asneeded. The process generally described above will be described more indetail hereinafter.

In place of using a single anhydrous liquid, a mixture of two or moreliquids may be employed, for example, liquid ammonia containing analkylamine having less than 8 carbon atoms, or pyridine. The solubilityof the metal formed as the result of the electrolysis in such mixedliquids is usually less than it is in the case of liquid ammonia alone,and the paste, hereinafter described, forms more readily. Othermaterials which will not interfere with the desired electrolytic actionmay be added to the solvent, if desired, provided that they do notdecrease the amount of the salt in combination with the anhydrous liquidto such an extent that the desired concentration of the salt cannot beobtained.

The use of an anhydrous liquid of the type described increases theadvantages of the use of a non-aqueous medium for the electrolysis ofalkali and alkaline earth metal salts and overcomes the objections thathave been encountered in --prior methods. Solubility of many of themetal salts is extremely high in this type of liquid and, as will bediscussed, concentrations can be reached in excess of any requirementsneeded for the economic production of the metal. Furthermore, byemploying the method described herein, the presence of water does notprevent the production of the metal and the process eliminates the waterfrom the nonaqueous liquid, as will be further discussed. While theelimination of the water consumes a small amount of electrical energy,the cost is nominal and the effect on the operation of the cell isslight. Furthermore, the cost of a liquid,

' such as anhydrous liquid ammonia, is low and I ance being ammonia.

the material is available in large quantities.

For convenience hereinafter, the process will be described in connectionwith the use of anhydrous liquid ammonia since this is the cheapest ofthe non-aqueous liquids available for use in the present process, andfor this and other reasons, it is used in the preferred embodiment ofthe invention. Furthermore, while, if desired, alloys or mixtures of twoor more of the alkali or alkaline earth metals may be prepared from asolution of two or more of the salts of the desired metals in theanhydrous liquid, the invention will be discussed from the standpoint ofthe preparation of a single alkali or alkaline earth metal.

As stated, the concentration of salt in the anhydrous liquid is animportant factor and in the process of the invention, the concentrationof salt in the electrolyte provides a medium in which the cathodeproduct is substantially insoluble. This permits the production of acathode product which is substantially iree from contamination byunelectroly-zed salt, and the cathode product removed from the cell inthe process of the present invention is to be contrasted with the impurecathod product which would result if a low concentration of salt in theliquid ammonia solvent were to be used. Such impure solutions are bluein color and comprise a small amount of metal, unelectrolyzed salt, andsolvent. As will hereinafter be discussed, the desired concentration ispreferably obtained by the use of the alkali or alkaline metal saltalone, but if desired, the required concentration may be obtained by theuse of another salt in conjunction with the alkali or alkaline earthmetal salt.

The cathode product separated from the unelectrolyzed portion of theelectrolyte may be in the form of a liquid or a paste or may be themetal itself, depending on the concentration of the electrolyte incontact with the cathode product and the operating conditions of thecell. The liquid is believed to be a blend or solvated compound betweenthe anhydrous ammonia and the metal, and an excess of ammonia may bepresent. In higher concentrations, some of the metal may be insuspension or in colloidal solution in the compound, and these liquidsmay contain up to about of the metal, the bal- When the concentration isstill higher, the paste is formed and in this case, it is believed thatmetal resulting from the evaporation of the ammonia from themetalammonia blend or compound is associated with that compound, and theconcentration of the metal in the paste usually exceeds about 90% andmay be as high as 99%. When the concentration of salt in the electrolytein contact with self will plate out on the cathode.

,uid is to be distinguished from a simple solution in which a lowconcentration of salt is dissolved in liquid ammonia. These diilerencesbetween the two types of liquids may be noted, for ex-' ample, if analkali Or alkaline earth metal is added thereto. In the case of liquidof the type used in the. present invention, a bronze liquid will beformed upon the surface of the liquid by a reaction between a smallamount of the ammonia in the liquid and the metal, such bronze liquidbeing immiscible in the liquid. When, however, an alkali or alkalineearth metal is added to a simple solution in which a low concentrationoi salt is dissolved in ammonia, the metal will dissolve in and bedistributed throughout the liquid, providing a blue coloration thereof.

The salt employed in producing the electrolyte is selected from thegroup consisting of they perchlorates and the thiocyanates. These saltsare stable and easy to prepare and may be obtained in an anhydrousstate, if desired, by simple drying procedures. Furthermore, theammoniumperchlorate or thiocyanate formed at the anode may be readilyreconverted into the alkali or alkaline earth metal perchlorate orthiocyanate by reaction with the oxide, hydroxide or carbonate of thealkali or alkaline earth metal. This reconversion may take place in thecell by adding the oxide, hydroxide or carbonate to the anolyte and theformation of the alkali or alkaline earth perchlorate or thiocyanatethen proceeds simultaneously with the electrolysis of the salt in thesame solution. However, since some water is formed by the reaction whichrequires additional electric current to dissociate it into itsconstituent parts, it will usually be desirable to treat the anolytewith the alkali or alkaline water can be present in a non-aqueouselectrolyte and not interfere with the preparation of metals that arehigher'than hydrogen in the electromotive series. This is unique and isto be compared with the attempts that have been made heretofore toproduce metals of this type in such solvents as acetone, acetonitrileand phosphorous oxychloride.

In general, the introduction of an alkali meta salt containing more than5% of water is not recommended and if water is associated with thesalt,it is advantageously below 1%. In the case of the alkaline earthmetal salts, the use of a salt'containing less than about 1% of water isdesirable and, the salt advantageously contains less than about 0.5%,.The alkali and alkaline earth metal salts, if they contain an excessiveamount of water or if the use of an anhydrous salt is desired, may bedried by any suitable method, for example, by the methods describedhereinafter in conjunction with the treatment of the salt obtained fromthe anolyte prior to its re-use in the cell.

The cell may be of any suitable design but is sealed by a lid or coverand is provided with a vent which permits the solvent vapor, thenitrogen generated at the anode and any other nonearth metal compound ina separate step. The halides do not possess the requisite solubility inammonia or other solvent to permit their use as theprimary source ofalkali or alkaline earth metal.

In the preferred embodiment of the invention, an anhydrous orsubstantially anhydrous salt is employed. However, limited amounts ofwater may be associated with the salt, if desired, without seriouslyaffecting the reactions that take place in the electrolysis of the salt,due to the fact that, as an initial step and before the metal platesout, the cell will purge itself of water. In purging itself of water,electric current is required and a sludge of the hydroxide of the metalwill be H stantially anhydrous salt. The type of salt employed and theease with which it may be dried are obviously the governing factors. Thewater content of. the salt should be kept lower in the case of alkalineearth metal salts than in the case of alkali metal salts due to the factthat there is a greater tendency for the alkali earth metal to reactwith the solvent to form amides or thelike, the reaction being catalyzedby the I presence of the hydroxide formed whenthe cell purges itself ofwater. Theimportant point to be noted in connection with the water isthat, in the pliesentinyention,,.a reasonable amount of condensable gasto pass out of, but will not permit moisture to enter, the cell; forexample, a mercury trap or a trap containing a moistureabsorbingmaterial inert to ammonia may be used. The cell may be constructed of awide variety of relatively cheap and available materials, for example,iron or steel, glass or enamelled material, rubber or syntheticrubber-like materials, and ceramics. This advantage itself makes theprocess of the present invention highly desirable as compared to othermethods in use for the production of alkali and alkaline earth metals. 7

' For most operations, it will be desirable to 'maintain a temperaturebelow the boiling point of liquid ammonia at atmospheric pressure (33.35C.) and, therefore, the cell will usually be provided with refrigerationmeans, for instance, refrigeration coils around the cell, or in theelectrolyte, or within the electrodes, the last named being preferred asthe heat is then removed at the point of its chief source. If desired,the cell may be a pressure cell, in which event refrigeration is notrequired, or the cell may be operated under conditions where theconversion of the liquid ammonia into the gaseous phase is relied uponto provide self-refrigeration of the cell. While in most operations, thetemperature of the cell, as stated, will be maintained by refrigerationmeans below the boiling point of liquid ammonia, the electrolysis can beconducted at much higher temperatures, for instance, where a very highconcentration of the alkali or alkaline earth salt is employed so thatthe. cathode product will be formed as a paste or a metal, temperaturesas high as 30 C. or higher may be used. Thus, a solution of sodiumperchlorate of relatively high concentration, for example 4.2 molar hasbeen employed with the result that bright metallic sodium metal has beenplated out on and adhered to the cathode.

The use of relatively low temperatures of operation, as contrasted withthose required in the processes employing a bath of molten salt,possesses several advantages in addition to the saving of the energyrequired to maintain the bath in a-fused state. For example, in theprocesses of the, present invention, there is no difiiculty 9ierioountered due to sublimation or vaporization of the metal from thecell and there is no d'ahger of:losing metal by burning. which is ahazard in v the production of metals'from molten "baths.

Furthermore; the use'of relatively low temperaturesifpermi'ts the cellto "operate 'isubstan'tially uniformly and without local electroderesistance,

and th'e uniformity of operation is 'enhanced by operating at a lowtemp'erature, for example, 7 below theboilingpoint of liquid-ammonia. l--'The cell may, except-as noted, be a 'c'onventiona'l electrolysiscellwith a 'cathode'x'and an anode, and the electrode'slimay'fbe otany-shape desired; 'such "as" fiatsheets rods, cylinders, or T the'-like; Sin'ce in -most instances; the' anode -product will bereactive-with the eathode prod uct a permeable"Ldiaphragm'} such "as a;porous 1 ceramicsheet, will usually beer'nployed to-divide the cellinto'- 'cathodeand anode compartments. 'lngthe cas'e o'i thethiocyanatesxhowever w here there is little or' 'n'o tendency forreaction with thecatho'de p'rodutit', the use of a-- diapl iragm is iil'ot feq il-ired.

T Th'e cathode*may be any ooii'dllb'to'ri for" exar'hple,pl'atinuinfiron; 7S1 er, eop 'erg' earbong and the llki- I i The anode i{p'r e'ferably rnade ot a I nateriaPtvl'iieh is 'siibstantially no-l"a'tive towardthe anode liiluor' tr'olytic carbon?-boromitireoriium,or tantalum. Of this g rouin oarbon -is' the preferid material. The'anode, howeverf inay, if desired, be of the typ'e 'that is reactiveWith the anolyte't for exampl'e, 'an' iron; nick'elg" copper; 'zinc, oralum-i num anode may be" usedi This second type=has not only thedisadvantage that-it is eonsu'mea "rela- "=tively rapidly; but also"that, when it is employed, the -anolyt'e'-k-zo'ntaii'iing' the *ammoniumsalt "will becoritaminated by a secondsaltivhichmus't be removed-in anadditional step-before the Values resem in the anolyte 'maybeuseda's thecell "feed. Referring" to the "electrical operating characteristic's ofthe 'cell,' while the 'eurrentdens'ity i's immaterial so far asoprabilityis concerned and thecell may *be operated at anycurrentdensity --aes1ree,:-a hasbe'en found-that th'epurrent dens'itiesre-lower thanrequiredanaqu ous systems. This is importantfrom thestandpoint of economy of operation and the dimensions of the cell: In "a-ty'p ical base, it is "entirely "feasible "to bperate cells infthefcom'mercialproductionof the metal mvabdut to 100 'ampere's -per"square 'deeimeter. Likewise, the voltage; may "be" Varied as" :desired,but'sincetheam'ount of voltageyisiadactor of the-power "cost-ibisadvantageouslykept as low as feasible'and it'has'-been"found"'tliatthe'"voltage may beabouthalfof"thatirequired -iii'othertypespfpro'c'esses making the'same'metalsl In -"'a'typical' -caseusingcurrent densities-with the range mentioned," the'volta'ge may be a'slowas 4 volts.

As stated;thecathdde product ;may be readily separated "therefrom; 1either periodically I when a sufficient amount has been produced ofcontinuously. The cathode roduct 'ifT'a .bronze' liquid or a"pa ste'may bereaduyprdc'essed obtain the free substantially puremetal'; merely'byremovin the ammonia associated therein by evaporatioriI Inthecaseofmetals of'low'melting *point such as" sodium',li'thium;"or potassium;this is readily accomplishedby evaporation atatem- -peratu'resuflicientto produce themetal in liquid state. 'J It-Lmayal'so be accomplishedbyevaporating the ammonia at a low temperature-which ==Iesu1ts Y in (a''spon'gy solid :mass -o'f metal. This S ration df lithium plumbidegleadmay-b espresso can be melted to form ahomogeneous-mass by .1 theapplication of I heat. The metals whiclrpossessshignmelting points;for'=example-calcium, strontium,- and "barium; 'may generally be most 5'readily. recovered from the bronze'liquid-or paste Iby evaporation in avacuum-stilloperating-at a temperaturesufficientlyt high so thatthe-metal can sublime and be re'covere'd. on -a "cooled con- -denser ina section of thestill.-- The recovery in "19 this fashion overcomesthe-difficulty of producing the metal in a pyrophoric state which'isusu- F ally the casefwhen' metals of high melting-point i:rare.-*rec'ove'red'by "drdinaryrevaporatidrrprocedure. I A furthermethod that-may be employed for the 1 5 :s'eparation. of the-"metal fromthe liquid product "is' "-to' p1 cipitatei= the material" out"chemically. fThis, in general, .ire'quiresr that the: precipitatingagent-"be miscible with the solvent present in the .liquid, although:this is not required in all-cases.

201 If a paste'iscobtainedas thecathode'produot or if the bronzesolution is too viscous fortl'iis' purpose;- additibnal amounts ofsolvent may be used to convert th'prodiictinto athir'rbronze or even ablue'solution; :Thus," for example, a solution .25 of calcium in liquidammonia inathe formpf a :blue solutiondue to the addition of liquid am---"monia to-a calcium-bronze liquid or paste: may

be treated' with toluene to precipitate the calciurrrfrom the -solutionin the-'form'ofva' spongy mass. Asecondexample ofthis type ofwp'rocedureis the precipitation of-lithium in finelydivided'formfrom-a--"-lithium-bronzesolution in i'liquielammonia bythe-addition of= an -amine, such as ,propyla'mine, in which -the metalis-"substan- .35 tially insoluble.

It is to be understood thatno limitation is to be placed on the methodof recovering the metal e sfromv thefbronze liquid or paste'andvgenerally the "methodwmployediwill be d'eterinin'ed' by the'economics and'the usefor'whi'ch the :metal-i's'pror'espondingto thedesired-form.

productionof alloys ina ehemieal ractieiig ln the production of alloys;roe" amplethe repawith thelithium bronze solution in -li'qu 13 inonia;and the l ammonia -subseduenn rated; Alloy s of l variousalkali and/earth metals may also be prepared merelyby mixiing: solutions ot the"desired metals f followed by evaporation-of the ammoniai' The :liquid er-pasty 'cathode produ'ct also' p'osse'sses hi'eh-"deg-ree offractivitylandyrmay, therefore, be-used' directly in chemical reactions;for exa'mple; asa pow'erful 1' reducing agent.

l t The?'liqui'd brrlpasty'kcathode product may be i-haindled withoiltdifiloulty and the conditions of -its =storage -Wi11- depen-d Ion theparticular metal. F or exam le; the p l 'oduot maybe's'tor :or enamelledcontainer :i...per, su'ch v glass,- -bein '-employed, or in' -iron ohtaihei sl "such as ca'stiromr'et orts, steel eyundersem the like Thepreeuct is relwhen the material is stored for long periods of time in aroom, a refrigerated or water-cooled container or compartment may beemployed to store the material. The product may be stored in pressurecontainers, if desired. By the use of cooled containers or pressurevessels, the ammonia or other solvent content of the product may beincreased, for example, the use of such containers or vessels isrecommended when a blue solution is prepared from the bronze liquid orthe paste.

Referring to the formation of the anolyte, the anions of the alkali oralkaline earth metal salt during the electrolysis move toward the anodeand when the electron charges of the anions are given up, the anions, inthe case an inert anode is used, react with ammonia to form the ammoniumsalt with the concurrent release of nitrogen gas. This may berepresented by the following equation where A- is the anion of the metalsalt:

(minus 6 electrons) 6A +8NI-I's- 6NH4A+N2 HA+S+ SETH-A- where I-IArepresents the acid of any anion A, Where S represents any solvent,where SH represents the solvated proton, and where A represents the acidanion. In the case of ammonia, the equation may be written as follows:

Therefore, it is evident that the addition or the formation of anyammonium salt to or in liquid ammonia forms precisely the same compoundin solution that is formed when free acid is added. Thus, for example,when ammonium perchlorate is dissolved in liquid ammonia, it dissociatesinto ammonium ions and perchlorate ions and thus is precisely the samething that happens when ipure anhydrous perchloric acid is added toliquid ammonia.

As stated, it is usually advantageous to place a porous diaphragm aroundthe anode so that, as the ammonium salt forms, it may be kept isolatedfrom the remainder of the cell and either periodically or continuouslydrawn off. The anode material removed from. the cell is a highlyconcentrated solution of the ammonium salt in the presence of some ofthe unelectrolyzed alkali or alkaline earth metal salt and is ideallysuited for use in converting alkali or alkaline earth metal carbonate,oxide or hydroxide to the metal salt for re-use as a cell feed. Thistreatment of the anolyte will be further discussed hereinafter.

The anolyte removed from the cell possesses a boiling point considerablyhigher than that of an anhydrous liquid ammonia. solvent and, in fact,in most instances possesses a boilingpoint considerably above roomtemperature. This is a further illustration of the different propertiesof the electrolyte used in the present invention as compared to anelectrolyte in which a low coni2 centration of salt is employed inliquid ammonia solvent.

When, however, instead of an inert anode, an anode, such as iron,copper, or nickel, which is attacked by acid, is employed, no free acidis produced but rather the metal salt of the acid. In the case of theuse of an iron anode, for example, the solution quickly develops a darkred coloration, due to the formation of an iron salt, immediatelyadjacent the anode. While the use of an inert anode is preferred, theuse of an anode such as an iron anode may be deemed to possess certainadvantages, for example, the condition of the anolyte can be visuallyobserved and there is no solvent waste due to the formation of nitrogengas. However, as pointed out, an additional recovery step is required toseparate the contaminating metal from the other materials, as will alsobe further discussed hereinafter.

In making up the original electrolyte, the alkali or alkaline earthmetal salt, either anhydrous or containing a small amount of water ashas been described, obtained from any suitable source, may be dissolvedin the anhydrous liquid to provide the requisite concentration. Oneconvenient method of obtaining a lithium salt, such as lithiumperchlorate, is to react calcium perchlorate and dilithium calciumphosphate (obtained, for example, by reacting dilithium sodium phosphatein an autoclave under pressure with lime in the presence of water)forming lithium perchlorate and insoluble tricalcium phosphate. Thelithium perchlorate solution is separated from the insoluble phosphateand the lithium salt is recovered from the solution and dried. Thismethod of obtaining a lithium salt is not claimed herein but is thesubject-matter of copending application Serial No. 666,187, filed April30, 1946, now Patent No. 2,548,037.

Various methods may be employed in the treatment of the anolyte toprepare it for re-use in the cell. For example, when an inert anode hasbeen used, the anolyte may be rendered suitable for re-use merely by theaddition of the desired amount of alkali or alkaline earth carbonate,oxide or hydroxide thereto. In general, however. it will be desirable toemploy a series of steps including a reaction in the aqueous phasebetween the ammonium perchlorat and the alkali or alkaline earth metalcarbonate, oxide or hydroxide. In such a procedure, the ammonia isremoved from the anolyte, by heating it necessary,

and the residue is dissolved in water and reacted with the carbonate,oxide, or hydroxide of the desired alkali or alkaline earth metal. Inthe case a carbonate is employed, ammonium carbonate is obtained as aby-product. The solution containing the alkali or alkaline earth metalsalt is then evaporated, advantageously after the addition of a smallamount of the acid of the anion to make sure that all the ammonia hasbeen removed and to serve as a make-up for any small loss of the anion.The salt recovered may be further dried if desired by any of the methodshereinafter discussed and is then mixed with anhydrous liquid ammonia toprovide a cell feed containing the requisite amount of salt. The ammoniainitially removed from the anolyte together with any other ammoniaavailable from other portions of the process, for example, that whichmay be evaporated from the cell, is collected and condensed and isreused, with a small amount of make-up ammonia, to prepare the cellfeed.

In the case the anode is not inert, the anolyte of themetal introducedto the anolytejby-the' anode, for example, ferric hydroxide.The-hydroxide i then-removed fromthe solution and the solution istreated with the carbonate, oxide or hydroxide as described.

In a typical case, in the production loin-1 0 pounds of lithium metalper hour, by a; cyolic=,-process,.;a cell having an iron-cathode, acarbon-;,ano.de,;and operating Witha. current density of 20- amperes persquare decimeter of electrode surfaceiisemployed. This cell requires18,000, amperes and operatesat 5 volts. The .feedto the cell {18 2, lquid comprisingv liqu d ammon a: .W c' rhi h; i combined lithium :nerhlorat rth canc r; atien being 2 mols of lithium-;;perchlorate;;per;l eof feed, and the rateof feedisqsuch that the -cell is supplied with; 54poun s o thium perchlorat perhour. tion containing 12 /2% c f,-; 1' .mclaligbalance iquid'a m n and fioat o electro rtei n is removed from thecell. The ammonia r is a te f o th brenz rso uti mce livered to thecompressor. contains ammonia, ammonium perchlorate, and lithiumperchlorate. Th liquidammonia is also evaporated from the product and isreturned to the compressor. "Water and lithium carbonate equivalenttothe ammonium perchlorate is then added to "the residue and ammoniumcarbonate is obtained as a by-product. Following evaporation of thesolution and drying of the salt, substantially-anhydrous lithiumperchlorate is obtained. In this example;approximately- 4%;; 0f thelithium perchlorate is recycled-as theresult of the presence of thissalt in the anolyte as it is removed from the cell. The necessary makeupammonia is added to the recovered liquid ammoniaand the .cell feed.isprepared. by mixing the required amount of lithium perchlorate andthe ammonia to provide a cell feed of the stated concentration.

As has been stated, the process is operative when limited amounts ofwater are associated with the alkali or alkaline earth metal saltdissolved in the anhydrous liquid solvent to form the electrolyte, but,in the preferred embodiment of the invention an anhydrous orsubstantially anhydrous salt is employed. In the processing of theanolyte to convert it into a material for re-use as the cell feed, thealkali or alkaline earth metal salt is dried and this drying reduces thewater content so that only a limited amount remains with the salt or itmay remove the water substantially completely.

In the preparation of the salts from aqueous media, it has frequentlybeen found desirable to crystallize, from a concentrated solution, acrop of hydrated crystals and then to subject them to dehydration, thusproducing a product which is nearly free from impurities. The motherliquor from this separation can be further concentrated to produce moreof the crystals and usually the mother liquor from several batches isaccumulated into one large batch which is treated as stated. It is alsopossible to prepare anhydrous salts in a manner similar to thatdescribed, for example, by mixing solid lithium carbonates with solidammonium perchlorate in the presence of Water and applying heat untilthe water is removed.

The salts may be dried by any suitable method at atmospheric pressure orunder a vacuum. The use of vacuum drying will result in the re-The-cathod rr si cti za-b nze:sel w Th e-anod produ mov,al -'of moistureeat --temperatul1es .plower can be used at atmospheric ipressurcnand 1117 211 case of thermally sensitive salts, the use of; yacuum drying maybe found to beiadrantageous. I

h p cu met od e ployedinthe dryin of the salt ,will depend ontheiextent-o f;dryness desired and the characteristics-of the part cular salt. Inthe case of the perchlorates,it'is-usually only necessary'to heat thematerial to a sufiicient temperature to drive out :allor .substantiall yall of the water. Thus, in the preparationof lithium perchlorate, thewet salt may-be;-heatedto, as.tem-.., perature of about 300'C.'and thencooleddown to room temperature in W ich-casethe material frozen to :asolid state can be brokenup .readily and dissolved in-the.solvent. In:the case :ofithe thiocyanates, which. are subject ,to thermal ,deecomposition, :other vmethods. areegenera'llyemployed.

One ofthe-methods whichemaysbecused -the production of ;a.substantial-lyanhydrous. 1358M],

where; there is .a: tendency tor the ;salt;being treated ,to decompose,:involves ;.the;rstep.rof am! moniating the partially .drie -d :salt :atlthensame' time that the -residu a1-..water. is, removed; =I his; isaccomplished, for instance,.x;by:passi-ngearnmonia gas,.; for;- example,that-which may .beeevolvedlas excess ammonia in the electrolysis vstep;(usually mixed with nitrogen). ,ovcrthepartiallw driedsalt.

which is maintained :at .an; eleyateditemperature. Thus,-;inthepreparation of lithium thiocyanate.

iorexample, the partiallyidried saltiiszplaced in a closed -contai-nermaintained .=:at,=a temperature in excess of about .150? -1C.iandzintocwhichlammania-gas is passed. vAfter:aiperioclof:time suflie;

cient :to drive outathe residual water; loweringnof the temperature willresult ;:in a ,vrelatively :zhot solution of lithium thiocyanate .inammonia-and, on cooling, this, solution ;ser.ves 58.5, 1 a highly con- 1centrated cell feed which can be added-i410 :the

0 1 in-i heliquid state or-canzbe further dilutedbefore its; addition to:the;cell. Alternativel-y,:the material can be treated by crystallizingthe ammoniated salt from the ammonia solution. This crystalline productmay then be used as a cell feed either directly or in a dissolvedcondition. Furthermore, this salt may be de-ammoniated to form ananhydrous salt if that should be desired.

For salts highly sensitive to thermal decomposition, it is also possibleto dry the salt from the frozen state at temperatures substantiallylower than the freezing point. In such a case, the drying is conductedunder conditions of high vacuum and the water sublimes from the solidmass.

Considerable modification is possible in the nature of the cathodeproduct, as well as in the conditions of the process and the structureand operative characteristics of the cell, without departing from theessential features of the invention, and it is to be understood thatsuch modifications and variations fall within the scope of the claims.

We claim:

1. A cyclic process for producing a metal selected from the groupconsisting of the alkali metals and the alkaline earth metals whichcomprises electrolyzing between substantially inert electrodes in a cella solution of a salt of said metal selected from the group consisting ofthe perchlorate and thiocyanate in an anhydrous liquid selected from thegroup consisting of ammonia, methylamine, ethylamine and pyridine toproduce a cathode product and an anode product, the concentration ofsalt in said anhydrous liquid at least in contact with said cathodeproduct being at least 2 mols of salt per litre of anhydrous liquid toprovide a medium in which the cathode product is substantiallyinsoluble; separating the cathode product from the electrolyte, wherebya cathode product comprising the metal substantially free from salt isobtained; separating the anode product comprising the anhydrous liquid,the anion of said metal salt and its associated solvated proton, SH+,where S is said anhydrous liquid, from the cell; reacting the anion ofsaid metal salt and its associated solvated proton with a compound ofsaid metal selected from the group consisting of the oxide, hydroxideand carbonate to form the corresponding metal salt, and utilizing saidmetal salt, in substantially anhydrous form, as source material in theprocess.

2. The process of claim 1 wherein said anhydrous liquid is ammonia.

3. A cyclic process for producing a metal selected from the groupconsisting of the alkali metals and the alkaline earth metals whichcomprises electrolyzing between substantially inert electrodes in a cella solution of ,a salt of said metal selected from the group consistingof the perchlorate and the thiocyanate in an anhydrous liquid selectedfrom the group consisting of ammonia, methylamine, ethylamine andpyridine to produce a cathode product and an anode product, theconcentration of salt in said anhydrous liquid at least in contact withsaid cathode product being at least 2 mols of salt per litre ofanhydrous liquid to provide a medium in which the cathode product issubstantially insoluble; separating the cathode product from theelectrolyte, whereby a cathode product comprising the metalsubstantially free from salt is obtained; separating the anode productcomprising the anhydrous liquid, the anion of said metal salt and itsassociated solvated proton, SH+, where S is said anhydrous liquid, fromthe cell; reacting in an aqueous medium said anion and its associatedsolvated proton with a compound of said metal selected from the groupconsisting of the oxide, hydroxide and carbonate to form thecorresponding metal salt; removing water from said metal salt to renderit substantially anhydrous; and utilizing said metal salt as sourcematerial in the process.

4. The process of claim 3, wherein said anhydrous liquid is ammonia.

5. The process of claim 3, wherein the metal produced is lithium,wherein the said metal salt is lithium perchlorate, and wherein the saidanhydrous liquid is ammonia.

6. The process of claim 3, wherein the metal produced is lithium;wherein the said metal salt is lithium thiocyanate, and wherein the saidanhydrous liquid is ammonia.

7. The process of claim 3, wherein the metal produced is calcium;wherein the said metal salt is calcium perchlorate, and wherein the saidanhydrous liquid is ammonia.

8. The process of claim 3, wherein the metal produced is calcium;wherein the said metal salt is calcium thiocyanate, and wherein the saidanhydrous liquid is ammonia.

LEONARD JOHN MINNICK. CYRIL PRESGRAVE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 788,315 Hoopes Apr. 25, 19051,538,390 Ewan May 19, 1925 2,313,408 Vingee et a1 Mar. 9, 1943 OTHERREFERENCES "Journal of Physical Chemistry, vol. 35 (1931), page 2289.

1. A CYCLIC PROCESS FOR PRODUCING A METAL SELECTED FROM THE GROUPCONSISTING OF THE ALKALI METALS AND THE ALKALINE EARTH METALS WHICHCOMPRISES ELECTROLYZING BETWEEN SUBSTANTIALLY INERT ELECTRODES IN A CELLA SOLUTION OF A SALT OF SAID METAL SELECTED FROM THE GROUP CONSISTING OFTHE PERCHLORATE AND THIOCYANATE IN AN ANHYDROUS LIQUID SELECTED FROM THEGROUP CONSISTING OF AMMONIA, METHYLAMINE, ETHYLAMINE AND PYRIDINE TOPRODUCE A CATHODE PRODUCT AND AN ANODE PRODUCT, THE CONCENTRATION OFSALT IN SAID ANHYDROUS LIQUID AT LEAST IN CONTACT WITH SAID CATHODEPRODUCT BEING AT LEAST 2 MOLS OF SALT PER LITRE OF ANHYDROUS LIQUID TOPROVIDE A MEDIUM IN WHICH THE CATHODE PRODUCT IS SUBSTANTIALLYINSOLUBLE; SEPARATING THE CATHODE PRODUCT FROM THE ELECTROLYTE, WHEREBYA CATHODE PRODUCT COMPRISING THE METAL SUBSTANTIALLY FREE FROM SALT ISOBTAINED; SEPARATING THE ANODE PRODUCT COMPRISING THE ANHYDROUS LIQUID,THE ANION OF SAID METAL SALT AND ITS ASSOCIATED SOLVATED PROTON, SH+,WHERE S IS SAID ANHYDROUS LIQUID, FROM THE CELL; REACTING THE ANION OFSAID METAL SALT AND ITS ASSOCIATED SOLVATED PROTON WITH A COMPOUND OFSAID METAL SELECTED FROM THE GROUP CONSISTING OF THE OXIDE, HYDROXIDEAND CARBONATE TO FORM THE CORRESPONDING METAL SALT, AND UTILIZING SAIDMETAL SALT, IN SUBSTANTIALLY ANHYDROUS FORM, AS SOURCE MATERIAL IN THEPROCESS.